Random phase detection in multidimensional NMR

Abstract

Despite advances in resolution accompanying the development of high-field superconducting magnets, biomolecular applications of NMR require multiple dimensions in order to resolve individual resonances, and the achievable resolution is typically limited by practical constraints on measuring time. In addition to the need for measuring long evolution times to obtain high resolution, the need to distinguish the sign of the frequency constrains the ability to shorten measuring times. Sign discrimination is typically accomplished by sampling the signal with two different receiver phases or by selecting a reference frequency outside the range of frequencies spanned by the signal and then sampling at a higher rate. In the parametrically sampled (indirect) time dimensions of multidimensional NMR experiments, either method imposes an additional factor of 2 sampling burden for each dimension. We demonstrate that by using a single detector phase at each time sample point, but randomly altering the phase for different points, the sign ambiguity that attends fixed single-phase detection is resolved. Random phase detection enables a reduction in experiment time by a factor of 2 for each indirect dimension, amounting to a factor of 8 for a four-dimensional experiment, albeit at the cost of introducing sampling artifacts. Alternatively, for fixed measuring time, random phase detection can be used to double resolution in each indirect dimension. Random phase detection is complementary to nonuniform sampling methods, and their combination offers the potential for additional benefits. In addition to applications in biomolecular NMR, random phase detection could be useful in magnetic resonance imaging and other signal processing contexts.compressed sensing | MRI

Improving resolution in multidimensional NMR using random quadrature detection with compressed sensing reconstruction

“…the same but selecting either the cosine or sine-modulated component at random for each time-increment, as suggested by Maciejewski et al (2011) ( b ). For comparative purposes, a and b are recorded for the same total experiment time; a is recorded with and b with .…”

Beyond Fourier

“…The concepts underlying NUS can be embraced more broadly, enabling NMR to stray from the constraints imposed by the Nyquist Theorem and the Jeener paradigm, to sparsely sample phase [69, 70] as well as time dimensions. One can imagine that sparse sampling approaches could productively engage with “single shot” methods [71] that sample space instead of time.…”

Nonuniform sampling of hypercomplex multidimensional NMR experiments: Dimensionality, quadrature phase and randomization

“…The majority of NUS schemes used to date collect all 2 d quadrature components for each sampled time point for quadrature detection conducted along d indirect dimensions. We recently described random phase detection (RPD, [26]), in which only a single quadrature component is randomly selected for detection from among the 2 d quadrature components, enabling a factor of 2 d reduction in the number of FIDs collected per time index, relative to conventional quadrature detection. RPD is one example of partial-component NUS , which as a class, includes any scheme that detects less than 2 d quadrature components for a sampled time point.…”